This invention relates to a novel helical dual-center engagement converting mechanism and its applications in fluid-powered actuation system, more particularly to a highly reliable, simple, powerful and balanced and less expensive helical rotary actuator. This actuator comprises a self-balanced linear/rotary dual-center engagement converter, compact porting systems, easy manufacturing modules, various body configuration and shaft interfaces with other components. This actuator also provides a rotary position control and backlash eliminating mechanism to meet high precision requirements with lighter weight, smaller size and higher accuracy of position and can be interfaced with different machines, such as subsea valves, earthmoving equipment, construction equipment, lifting equipment, landing gears, militarily equipment and robotic and medical devices, artificial arm and leg joints.
Conventional fluid-powered helical actuators have been used in many industries for years, it is based on an old helical linear/rotary converter mechanism and includes a cylindrically shaped housing and two moving parts: a shaft and an annular piston. Helical spline teeth machined on the shaft engage a matching complement of splines on an inside diameter of the piston, an outside diameter of the piston carries a second set of helical splines that engages a ring gear integral with the housing. While conventional linear pistons with pivot joint, the rack and pinion and vane actuators still have majority market share over the helical rotary actuators, the reason is that conventional fluid-powered helical rotary actuators have many unsolved problems and disadvantages; (1) low efficiency, about 60%-70% efficiency for helical rotary actuator is in comparison with that of 90 to 98% for the rack and pinion or vane actuators, so it prevents the actuator from low pressure applications, there are fewer helical pneumatic actuators in the market in comparison with rack and pinion and vane actuators, it not only wastes lot of materials and energy but also can not be used for limited space or restrict weight applications (2) high unbalanced thrust, the unbalanced thrust is still an unsolved problem, it requires more internal parts to balance the thrust, so length of actuator becomes very longer, size of the actuator becomes bigger even there are some balanced helical actuators in the prior art, none of the trials has been commercial success (3) backlashes, due to cumulative clearances of two sets of helical teeth engagements, it increases the impact on the teeth and reduces the accuracy of moving position, life of actuator, some efforts were made in the prior art, but none of trials has been commercial success (4) high stress concentration on cylindrical bodies with helical teeth either by pinging, welding or integrating, it has been struggled for years to seek the solution, under high pressure 3000-5000 psi, the root of helical teeth on cylindrical body generates high stress concentration, this structural problem not only reduces the load capacity and increase the actuator size and weights, but also it can cause sudden break down based on Paris law and is considered to be unreliable and unsafe for critical operations where linear piston with pivot joint devices which have the same rotation function still play a key role in earthmoving equipment and landing gears (5) restrict installation position, most helical actuators are designed for either vertical or horizontal position, they are not suitable for any position between them, due to lack of proper structure and bearing (6) lack of position control, due to lack of control of rotary position and fail to close or open function, it prevents the actuator from critical applications such as military equipment, robotic devices and valve control (7) lack of interface function, most of the actuator bodies are cylindrical shape, such a shape is difficult for three dimensional joint (8) low reliability, according to Failure Modes and Effects Analysis (FMEA), a piston with internal and external helical teeth has the highest severity, with lack of redundancy, the conventional helical actuator never can compete with linear piston with pivot joint in critical applications like landing gears (9) structural inferiority (a) most cylindrical body can not sustain high structural bending load and compression load, it prevent it from those applications like rotation with high bending or compression (b) material incomparability, since material requirement of mechanical property for body is very different from that of teeth, for the body, it requires high strength, ductile, while for the teeth, high hardness and wearing resistance are the key requirements, since the helical teethes are a part of the body, so most designs are to put the body strength first and to scarify teeth design, as a result the teeth with soft surface will be damaged first or wore out fast even with hydraulic fluid (10) difficult and expensive manufacturing, it is difficult and expensive to make helical teeth, specially internal helical teeth or internal splines on the body as an integral part, it not only makes the manufacturing process more difficult if not impossible, it is impossible to replace the teeth alone, since there is no modulization design in the actuator, conventional actuator manufacturing require large inventory for each size actuator (11) inlet and outlet ports are far away and not standardized, so it is difficult to connect the ports, especially in case of counterbalanced valve is required, additional tube and adapter is needed, it not only increase cost but also reduce reliability, any addition joint adapter and tube can cause leak.
In order to overcome the disadvantages or solve the problems of the conventional fluid-powered helical rotary actuators, many efforts have been made in the prior arts. There are four approaches to improve the conventional helical actuators in the prior arts, but those approaches work against each other within a limited scope.
The first approach is to improve the conversion mechanism. U.S. Pat. No. 3,255,806 to Kenneth H. Meyer (1966), U.S. Pat. No. 4,089,229 to James Leonard Geraci (1978) show a approach is to use a number of keys and keyway to prevent the piston sleeve from rotation under linear force, this conversion mechanism did work, but there were two drawbacks, one is to waste large internal body space due to the keyway, the other is to cause high stress concentration on the body, under 3000-5000 psi pressure, such stress condition is unsafe and prohibited, likewise other actuators are provided with splined design to prevent the piston from rotation for valve actuations, in addition, it is expensive to make, so many other solutions came out like U.S. Pat. No. 1,056,616 to C. E Wright (1913), U.S. Pat. No. 6,793,194 B1 to Joseph Grinberg (2004) the approach is to use two bars to prevent piston sleeve from rotation, the drawback is to waste a large interior housing space and it is restricted to smaller actuator applications, finally current widely acceptable helical actuator is shown in U.S. Pat. No. 3,393,610 to R. O. Aarvold (1966) disclosed a device with a pair helical gearing means between a housing and a shaft in an opposite direction, but it did not prevent the piston rotation, rather it is used as medium to generate a reaction torque between the housing and the shaft and in turn to rotate the shaft, the drawback is to waste internal space and more energy to rotate the piston and increase backlash and cost, a desirable design for this conversion mechanism is that only rotary part should be a rotary shaft, not a body or a piston, moreover the additional rotation will wear bearings and o rings faster and more than under a linear movement only, in addition the arrangement greatly restricts an engaged diameter of the piston, as a result, the output torque is greatly reduced, again, high stress concentration on the body still exists, even it become more difficulty to manufacture with internal and external teeth in a piston.
The second approach is to balance thrust force and ease consequences of the unbalanced forces on helical actuators, U.S. Pat. No. 3,255,806 to Kenneth H. Meyer (1966) shows an actuator with two actuator assembled in an opposite teeth and direction, the design become more difficulty for machining the keyways on the longer body, other effort made is shown on U.S. Pat. No. 4,745,847 to Julian D. Voss (1988) discloses a new design with four parts; a shaft, a housing, a linear piston, a rotation piston, it causes more leak paths and make the actuators more complicated and less reliable, finally U.S. Pat. No. 3,393,610 to R. O. Aarvold (1966) shows two sets of helical teeth in an opposite direction on a piston, it balances the thrust force on the piston but not on the shaft or housing, this arrangement causes a constant tension on the piston during linear/rotary converting, so the piston is subject to torsion well as tension while the load is still applied to shaft and housing, as a result the size of piston is increased while the housing and shaft are underused, so far there is no successful full balance design in the market.
The third approach is to simplify the manufacturing process, there is few development in the field, the most internal helical teeth are as an integral part of a housing or shaft, few welding process or pining process have been tried, but for the current pressure vessel safety standards, those practices under 3000-5000 psi pressure are considered to be unsafe, so stronger, heaver body or shaft with a integral helical teeth are only the solution for now, there is no improvement in the filed
The fourth approach is to ease the backlash and improve performances of the actuator, a typical example is shown in U.S. Pat. No. 2,791,128 to Howard M. Geyer (1957) and U.S. Pat. No. 4,858,486 to Paul P. Meyer (1989), a complex mechanical adjustable devices are introduced, but in most applications, such a design is considered to be impractical or too costly due to inherent disadvantage of clearance of two set of helical teeth, the fundamental adjustment mechanism is still unchanged.
So the fluid-powered actuation industry has long sought means of improving the performance of fluid-powered actuation system, eliminating the unbalanced thrust increate efficiency, increate integrity of the body strength, and increasing reliability and accuracy rotary position with less cost.
In conclusion, insofar as I am aware, no fluid-powered actuation system formerly developed provides higher system performances with a modularization structure, less parts, highly efficient, versatile, reliable, easy manufacturing at low cost.